'Regret' is literally 'to weep again and again' — Scots 'to greet' still means 'to weep,' preserving the root.
A feeling of sadness, repentance, or disappointment over something that has happened or been done.
From Old French 'regreter' (to bewail, to lament the dead), possibly from Frankish *grētan (to weep), related to Old English 'grǣtan' (to weep) and Old Norse 'gráta' (to weep), from Proto-Germanic *grētaną (to weep, to cry), likely from PIE *gʰreh₁d- (to cry out). The 're-' prefix intensifies the action: to regret is to 'weep again and again' over what has passed. In Old French the word was specifically used of lamenting the dead